CALCIUM AND PHOSPHORUS IN" THE FEED OF DAIRY COWS. 3 
the test cows were better bred, but a part also is due to the larger 
quantity of feed they consumed. How much of the increased milk 
yield to attribute to each of these factors is a question of great prac- 
tical interest. 
STANDARD RATIONS INSUFFICIENT FOR OPTIMUM MILK YIELD. 
The cycle of lactation consists of two phases which may be called 
the preparatory and the active phases. Considerable changes go 
on in the udder of a cow for some time before her calf is born, and 
usually make themselves manifest by an increase in size and con- 
gestion of that organ. There is no doubt that the amount of the 
subsequent milk yield largely depends on these changes, and it is 
highly probable that the changes themselves depend on the state of 
nutrition in which the animal happens to be for the few weeks 
before her calf is born. 
JAN. 
1919 
e 
10 
a 3 4 5 6 7 
HUNDRED POUNDS OP MILK 
Fig. 1. — Influence of the length of the dry period on the subsequent milk yield in the case 
of cow 17. The columns represent the pounds of milk given in the first clear calendar 
month after calving in the years indicated. Before calving in the years 1914 to 1917, 
inclusive, this cow was fed the routine ration for dry cows at Beltsville ; her dry periods 
averaged 44 days. Before calving, in December, 1918, she was given a dry period of 122 
days and fed approximately as in her previous dry periods. 
It is well known that animals are capable of storing up large 
quantities of nutritive material in times of plenty and using these 
stores in times of stress. The effect of the feed on milk secretion, 
therefore, often may be long delayed and rather complicated. It is 
not at all impossible that the effects of a deficient ration supplied 
in one lactation period may not show themselves until the subsequent 
period or even later. 
Figures 1 and 2 give graphically the histories of two cows which 
were brought to the Beltsville farm some years ago and fed and 
treated according to the usual routine. The milk yields fell off very 
